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 A056723 Numbers k such that 8*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
 1, 7, 23, 29, 133, 173, 367, 1925, 3707, 5765, 9709, 19573, 43753 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that (25*10^k - 1)/3 is prime. LINKS Table of n, a(n) for n=1..13. Makoto Kamada, Prime numbers of the form 833...33. Index entries for primes involving repunits MATHEMATICA Do[ If[ PrimeQ[ 8*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A093676. Sequence in context: A095314 A038948 A019389 * A080802 A078515 A225822 Adjacent sequences: A056720 A056721 A056722 * A056724 A056725 A056726 KEYWORD nonn AUTHOR Robert G. Wilson v, Aug 11 2000 EXTENSIONS Corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 19573 and 43753 from Serge Batalov, Jan 2009 confirmed as next terms by Ray Chandler, Feb 13 2012 STATUS approved

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Last modified February 22 18:56 EST 2024. Contains 370260 sequences. (Running on oeis4.)